Thrombocyte counts after 5 Gy TBI (day 0) for monkeys treated with TPO 5 μg (▪, n = 4), TPO 50 μg (□), TPO 0.5 μg (○, n = 2), and the concurrent placebo treatment (▵, n = 4). The lower shaded area represents the mean ± SD of 12 control monkeys; the upper shaded area is the mean ± SD of 4 monkeys treated with human TPO for 21 days after irradiation. Data represent the arithmetic mean ± SD of the various treatment groups. The horizontal line defines the level of thrombocytopenia (40 × 10⁹/L) below which thrombocyte transfusions are given.